Requirements:

1. nutritional factors
2. energy and carbon source
3. environmental factors

1. Carbon
2. Oxygen
3. Nitrogen
4. Hydrogen
5. Phosphorus
6. Sulfuer

Less amounts of: K, Mg, Ca, Fe

Trace amounts of: Mn, Co, Cu, Mo

Amino Acids (for proteins)

Purines and Pyrimidines (for nucleic acids)

Vitamins (for certain enzymes)

Energy and Carbon Source

Two sources of energy: Chemical and Light

[image]

Two sources of carbon: CO₂ and Organic Compounds

pH

Temperature

Oxygen

pH (Environmental Factor)

[image]

Acidogenic Bacteria = produce acids; some may make their own environment harmful to themselves

Aciduric Bacteria = can tolerate low pH although it is not their optimal pH for growth

[image]

[image]

[image]

Physiological and structural adaptations are related to temperature

• Psychrophiles produce enzymes with lower temperature optima.
• Psychrophiles have higher content of unsaturated fatty acids in membrane lipids that increase fluidity.
• Thermophiles have enzymes that are heat-stable; ribosomes work at higher temps; also more salt bridges in proteins.
• Thermophile membranes have many long-chain fatty acids with more saturated fatty acids.

Temperature in the oral cavity is rather constant (35-36°C); during active disease, the periodontal pocket can get up to 39°C.

• Some organisms require O₂
• Some organisms are killed by O₂
• Some organisms are not affected by O₂

[image]

Classes of Bacteria based on Oxygen Requirement

Obligate aerobes

• grow only when oxygen is present (ambient concentration of 21%)
• use O₂ as a final electron acceptor in aerobic respiration
• no fermentation

Faculative anaerobes

• grow with or without oxygen
• under anaerobic conditions: fermentation or anaerobic respiration
• under aerobic conditions: aerobic respiration

Aerotolerant anaerobes

• grow equally well with or without O₂
• are exclusively fermentative but not sensitive to the presence of O₂
• lack catalase, but have superoxide dismutase (SOD)

Obligate anaerobes

• either killed or growth is inhibited by presence of oxygen
• toxic byproducts (O^2-·, H₂O₂, OH·) react indiscriminately with any organic molecules, including DNA and proteins
• absence of enzymes such as SOD, catalase and/or peroxidase, which get rid of radicals
• are exclusively fermentative

Microaerophiles

• won't grow at normal atmospheric oxygen level (21%), but require some oxygen for growth (2-10%)
• aerobic respiration
• reduced amounts of catalase and SOD

Capnophilic

• require 5-10% of CO₂ for growth

[image]

Oxygen and the Oral Cavity

• Oral cavity contains few, if any truly aerobic species
• Most are faculative anaerobes (e.g. Streptococcus, Actinomyces, Neisseria) or obligate anaerobes (e.g. Peptostreptococcus, Veillonella)
• Some microaerophilic species (e.g. Campylovacter) and capnophilic species (e.g. Aggregatibacter actinomycetermcomitans)
• Anterior surface of the tongue: 16.4%
• Posterior surface of the tongue: 12.4%
• Buccal folds of upper and lower jaw: 0.3-0.4%
• Plaque: surface = high oxygen, bottom layer (tooth surface) = anaerobic
• Subgingival plaque = anaerobic
• Drug of choice: metronidazole